1. Field of the Invention
The present invention generally relates to superconductors, and more particularly to a d-wave quantum bit which permits large-scale integration of quantum bits for use with quantum computers.
2. Description of the Related Art
A practical design of a quantum computer requires hundreds to thousands of quantum bits (xe2x80x9cqubitsxe2x80x9d), but up to now realizations of qubits by methods such as nuclear magnetic resonance (NMR) seem unsuitable for the miniaturization required to enable a many-qubit machine to be constructed at reasonable cost (.g., see Gershenfeld, et al. Bulk Spin-Resonance Quantum Computation, Science, Vol 275, pp 350-356 (1997) and Chuang et al. Experimental realization of a quantum algorithm Nature Vol 393, pp 143-146 (1998), incorporated herein by reference).
Quantum computers promise enormous speed. However, quantum computing can only be realized if the quantum computing device (quantum computer, quamputer) is built on a scale of at least several thousand qubits. The inherent scalability of solid state devices and the high level of expertise existing in conventional industrial electronics and experimental mesoscopic physics make solid state-based quamputers an attractive choice.
Quantum coherence preservation (e.g., maintenance of the quantum state for any useful time period) within a single qubit, is a major problem, also when several qubits are placed in close proximity, they tend to electromagnetically interfere with each other and destroy any charge/signal which is stored in adjacent qubits.
The macroscopic coherent ground state and gapped excitation spectrum in superconductors are favorable situations for coherence preservation. As discussed in greater detail below, the invention comprises a qubit implementation in solid state integrated circuit technology which can support LSI (Large Scale Integration). The quantum computer chip is operable at very low (milliKelvin) temperatures, which are required to ensure purity of quantum states and to minimize noise.
It is, therefore, an object of the present invention to provide a structure and method for a d-wave qubit structure that includes a qubit disk formed at a multi-crystal junction (or a superconducting qubit ring) and a superconducting screening structure (e.g., ring or disk) surrounding the qubit. The structure may also include a superconducting sensing loop, where the superconducting sensing loop comprises an s-wave and/or d-wave superconducting ring. The superconducting screening ring may include at least one weak link, driven to the normal state by a means such as a superconducting field effect transistor, or a laser beam.
The multi-crystal junction comprises a junction (e.g. disk) of differently aligned controlled orientation high temperature superconductor crystalline structures or a superconducting ring. The relative orientations of the grains of the crystalline structures are chosen such that the superconducting screening ring spontaneously generates a half-integer quantum of flux at some or all of the grain boundary intersection points. The superconducting screening ring comprises one of cuprate, niobium or lead. The invention also includes an array of such quantum bit structures and a quantum computer including the quantum bit structures